The present invention relates to security systems for detecting intrusion into protected areas such as automobiles, and more particularly to sensor devices for detecting such intrusion events to an automobile such as motion, shock/vibration or glass breakage, wherein the sensitivity of the sensor device to motion and shock alarm events is conveniently programmable by the automobile operator.
Security systems for automobiles are in common use today for protecting against unauthorized entry into the vehicle and sounding an alarm in the event of detected intrusion events. The systems include trigger and sensor devices for monitoring the status of doors and other entry points such as the hood and trunk, and may include sensor devices for detecting motion or shock/vibrations to the vehicle and even sounds such as glass breakage. Thus, the sensor may be adapted to detect shock/vibration resulting from actions such as attempted forced entry, glass breakage, jacking or lifting of the vehicle, driving the vehicle, or the like.
A common problem affecting conventional security systems is that of false alarms set off by environmental conditions unrelated to an attempted intrusion into the vehicle. In all systems on the market today, the sensor devices employed with the system have either a fixed sensitivity level, i.e., the threshold motion or shock level resulting in a detected alarm condition is fixed, and may neither be adjusted by the system installer nor by the vehicle owner, or sensor devices wherein the sensitivity may be adjusted by the installer of the system but not, however, by the user. Typically these sensor devices employ self-resonating circuits which trigger an alarm when the resonating energy reaches a certain threshold level, which may be adjusted by the installer. The adjustment is typically by a screwdriver and made on a screw head on the sensor housing. Since the sensor is typically installed at a hidden location which may not even be known to the owner of the vehicle, the installer is generally the person who adjusts the sensitivity level of the sensor. This preset level is therefore not readily adjustable, except by returning the vehicle to the installer, and even then the change in sensitivity may not be correct for the particular conditions of the parking location of the vehicle. For example, the vehicle may be parked routinely in a multilevel parking structure, an environment in which a relatively high level of low frequency high amplitude vibrations and movement may be present. If the installer adjusts the sensor in a ground-level (stable) garage, the resultant sensitivity level may be too high, resulting in false alarms once the owner begins parking the vehicle in the multi-story parking structure, or on a street with heavy traffic that will cause both high level of vibrations and substantial displacement of air by passing large vehicles such as busses and trucks, thereby causing the parked car to sway, consequently causing false alarms. As a result, the owner may elect not to arm the system when parking in such a location. Yet, such intermittent parking locations may be the higher risk situations, so that if the owner decides not to arm the system in such locations due to the high false alarm occurrence, he faces much greater risk of unauthorized intrusion into his vehicle.
Conventional glass breakage detectors are also susceptible to high false alarm rates. Conventional glass detectors typically operate on the principle of tuning the detector to the glass breakage frequency in the range of 10-12 Khz, and generate an alarm condition when the total energy detected at that frequency exceeds some threshold which is set by the installer. Such detectors often generate alarm signals when a siren-sounding vehicle, such as an emergency vehicle, passes a parked vehicle employing such a conventional glass breakage detector, or whenever a jet or helicopter flies low over the vehicle when it is parked in the proximity of an active runway near an airport.
It is therefore an object of the present invention to provide an intrusion event sensor which may be quickly and conveniently programmed by the user to a desired alarm sensitivity level without any tools, knowledge of electronics, or the knowledge as to where the sensor is installed in the vehicle.
A further object of the invention is to provide a sensor which is far less susceptible to false alarms than conventional sensor devices.